radv: fix loading 64-bit GS inputs
We have to load 2 32-bit integer and to cast correctly.
This fixes crashes with gs-double-interpolator.vk_shader_test.
Cc: 19.2 mesa-stable@lists.freedesktop.org Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111734 Signed-off-by: Samuel Pitoiset samuel.pitoiset@gmail.com